Pressure control apparatus



Dec. 23,1947. 1 SPARROW 2,433,326

,PRESSURE CONTROL APFARATUS Filed May 19, 1944 f 2 Sheets-Sheet l Gttorneg Decs 23, 1947. H. T. SPARRCW 2,433,325

PRESSURE CONTROL APPARATUS K Filed May 19, 1944 2 Sheets-Shed. 2

Patented Dec. 23, 1947 UNITED STATES PATENT oFFlcE Hubert '1'. Sparrow, Minneapolis; Minn., assignor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn., a corporation of Delaware Application May 19, 1944, sensi Nasssn 12 claims. (ci. 23o-5) 4 This invention relates to improvements in apparatus for controlling the discharge pressure of the turbine operated, supercharging compressors used for supplying air under compression to the intake manifolds of internal combustion engines.

It is the practice, particularly in the case of aircraft engines, to provide a turbo-supercharger unit for boosting the pressure of the air for combustion in order to increase the power of the engine and maintain a desired power output condition regardless ofthe variations in atmospheric pressure encountered at different altitudes. For this purpose a compressor, called the supercharger, is used and it is operated by a turbine powered by the exhaust gases from the engine. To control the speed of the turbine and compresser, and hence the pressure of the air discharged from the latter, the pressure and effect of the exhaust gases on the turbine is controlled by a damper or valve, known as the waste gate, which when opened allows the exhaust gases to escape freely to atmosphere and which, when progressively closed, diverts more and more of the gases to' the turbine to increase the speed thereof.' The position of the waste gate is thus seen to precisely govern the pressure ofthe air ldelivered to the engine.

For positioning the waste gate reversible electric motor may be used, controlled by an electronic amplifier, which in turn responds to several controlling conditions to actuate the motor. Thus there may be a manual control by which intake manifold pressures may be selected and a pressure sensing or responsive control which will then operate to maintain the selected pressure within close limits, regardless of the changes in pressure of the air taken into the compressor as the aircraft 'flies at different altitudes. Such control lsystems are disclosed in detail in my copending sole application Serial No. 476,797, filed February 22, 1943 and in my co-pending joint application with Robert J. Kutzler Serial No. 486,992, filed May 14, 1943.

During operation at the higher altitudes especially, and whenever intake manifold pressure of the higher values are selected, the waste gate 1s necessarily near a. closed position. Under such conditions the waste gate position is very critical due to the fact that the exhaust back pressure is then quite high and the turbine-compressor speed is near the highest safe values. Any failure or mismanagement of the operation of the system is then likely to cause the intake manifold pressure to exceed a safe value, causing damage to the engine; or it may cause over-speeding of the turbo-supercharger or the building up of excessive exhaust back pressure to reduce engine eilciency. Any of these malfunctions might very readily result in disaster to the aircraft and its occupants, particularly in military uses.

It is the custom in control systems of the type herein considered to provide means embodied in the electrical circuit for limiting the velocity and ratel of acceleration of the turbo-supercharger unit to 'safe values, and also to limit the amount of compression which may be called for by the pilot or engineer. ture such limiting means are subject to bothelectrical and mechanical failure, las well as a slight lag, characteristic of the circuits necessary, in their response to an overboost condition, as it is known to thev art. It is possible therefore that even with such controls the pressures may reach a dangerous value.

It is the primary object of my present invention to provide means responsive to the discharge pressure of the supercharger for promptly and effectively reducing the operating speed of the turbinewhe'n such pressure exceeds,'even momentarily, a predetermined maximum safe value, and to provide means of such nature which is purely mechanical and forms no part of the electrical control system, so that 'it will operate independently of any failure therein. Another object is to provide an overboost limit or control means for this purpose which operates to relieve the exhaust gas pressure upon the turbine and thus exert the most effective control on the speed thereof and over the pressure at the discharge side of the compressor. A further objectv is to provide a high limit discharge pressure control for the superchargerwhich will positively override the call o f the electronic or electrical control system for pressure above the selected safe maximum value. f l

Other objects and advantages of my invention will become apparent from a consideration of the appended specification, claims and drawings. In the drawings:

Fig. 1 is a diagrammatical showing of a complete engine, induction and exhaust system, the electronic control for the intake manifold pressure, and one form of my means for preventing overboost in the compressor discharge pressure.

Fig. 2 is a somewhat diagrammatical showing of a modification of the overboost control.

Fig. 3 is a similar view of still another modication.

Referring now more particularly to Fig. 1, I show therein an engine I0 which may be the However, by their very nal .bustion in the engine passes from an intake II through a compressor I2, a conduit I3, an aftercooler I4, a conduit I5, a throttle I5, a carburetor I1, a conduit I5, a direct driven compressor I9, a conduit.25, and an intake manifold 2l into the engine.

The exhaust gases from the engine issue from an exhaust manifold 22 and are discharged through a duct 23 having a branch 24 leading to a turbine 25. The turbine is provided with an outlet 25 through which the exhaust gases may escape to atmosphere after passing through the turbine. The conduit 23, commonly termed the exhaust stack, also has an outlet 21 to atmosphere, and controlling the flow of exhaust gases from this outlet is a damper or valve 25 known as the waste gate.

The compressor i2 is driven from the turbine 25 through a shaft 29 and the air compressed in this compressor I2 passes through the aftercooler I4, wherein the heat of compression is at least partly removed by passing fresh air from an intake 30 in heat exchanging relationwith the compressor discharge air, after which the cooling air is delivered at the outlet 3l.

The throttle I may be adjusted by the hand control 32, and in the carburetor I1 fuel from a supply (not here shown) is mixed with the air to form a combustible gas.

The compressor I9 is directly driven from the engine by shaft 33 and is utilized not only as a compressor but also to evenly distribute the mixture of fuel and air to all cylinders of the engine.

The waste gate 25 is driven by a motor 34 through a gear train 35. TheV motor 34 is of the split phase type. being provided with a pair of field windings 36 and 31 which are spaced ninety electrical degrees apart, and an armature 35. The field winding 31 is supplied with electrical energy from a secondary winding 39 of a transformer 40 having a-primary winding 4i which is connected to a suitable source (not shown) of alternating current. The energizing circuit for the winding 31 may be traced from the lefthand terminal of the transformer winding 3 9 through a conductor 42, a condenser 43, the eld Winding 31, and a conductor 44 to the right-hand terminal of the secondary winding 39.

I'he flow of electrical energy to the motor field winding 36 is controlled by an electronic amplifier 45 to which the winding is connected by conductors 46 and 41. The amplifier 45 is powered from another secondary winding 45 on the transformer 4U, to which the amplifier is connected through conductors 49 and 55.

'I'he amplifier 45 is provided with a` pair of input terminals 5I and 52 and operates to supply the field winding 35-of the motor with alternating current the phase of which depends upon the phase of an alternating current signal impressed across these input terminals'5l and 52. Any suitable form of amplifier may be used, but I .prefer to employ one of the type shown in Fig. 1 of the so-pending application of Albert P. Upton, Serial No. 437,561, filed April 3, 1942, now matured into Patent No. 2,423,534 of July 8, 1947.

t will be evident that if-the motor field winding 35 is supplied with alternating current which leads the current in the other field winding 31 by ninety electrical degrees th'e motor will rotate in one direction, whereas if the current in winding j35 lags the current in winding 31 by this amount, the motor will rotate in the Opposite direction.

f The phase of the signal applied to the amplifier -.input terminals 5I and 52 is determined by the electrical conditions existing in a compound network which consists of three separate networks connected in series. The circuit between the amplifier input terminals may be traced from terminal 5I through a conductor 53. a first electrical network 54, aconductor 55, a second electrical network 55, a conductor 51, a third electrical network 55, and a conductor 55, back to the input terminal` 52.

The network 55 includes a transformer 50 having a primary winding 55a and a secondary winding 55h across the terminals of which is connected a slidewlre resistance 5I by means of conductors 52 and 53. 'I'he conductor 55 is connected to a slider 54 which cooperates with the resistance 5I and which is adjustable thereacross by means of a control knob 55. The resistance 5I and slider 54 together form a control point adjuster 55 0r manual selector for the intake manifold pressure control system.

Another slidewire resistance 51 is connected across one-half of the transformer secondary winding 50h by a conductor 55 connected to a lower terminal thereof and a conductor 59 connected to a center tap on the winding. A slider 15 cooperates with the resistance 51 to form a Calibrating potentiometer designated generally at 1l. 'I'he center tap of the winding 55 is connected by a conductor 12 to the center of the resistance 6I t0 decrease the impedance between the sliders 54 and 15.

The network 55 comprises a transformer 13 having a primary winding 13a and a secondary winding 13b across the terminals of which is connected a slidewire resistance 14 by means of conductors 15 and 15. Cooperating with this resistance 14 is a slider 11 which is connected to slider 15 by a conductor 51. The slider 11 and the resistance 14 together form a main pressure controller represented generally at 15, and this controller is adjusted in accordance with the pressure in the induction system of the engine. For this purpose a pressure take-ofi duct 19 is connected to any suitable point between the supercharging compressor I2 and the engine, and is here shown as connected to the duct I5 leading to the throttle I5. The duct 15 conveys the air pressure to the interior of a bellows 55'. A second bellows 5l is evacuated and the two bellows 55 and 5I are supported with their free ends extending toward each other at opposite sides of the slider 11. These free ends are connected by link 52 to each other and to the slider 11 so that expansion and contraction of the bellows 55 in response to fluctuations in air pressure therein will shift the slider along the resistance 14. The evacuated bellows 5I compensates this controller for variations in atmospheric pressure in a well known manner. l

A second slidewire resistance 53 is also connected across the winding 13b by means of conductors 54 and 55, and cooperating with resistance 53 in a slider 55 which is positioned in accordance with variations in the rate of acceleration of the turbine 25. For this purpose there is schematically shown a control device 51 connected to the operating shaft of the turbine, and the resistance 53 and slider 55 together form an acceleration compensating controller 55. It may here be noted that the slider 55 will normally remain in the position shown upon a dead spot 59 at the left-hand end of resistance 53, but will swing to the right upon the acceleration of :,sasac y nected to the slider 85 by the aforesaid conductor 55. The slider 94 and resistance 9| cooperate to form a velocity responsiveL compensating controller 95, and the slider 94 is positioned by a velocity responsive control device 95 connected to and operated by the'turbine 25. The slider 94 is moved over the dresistance 9| by the control device 98 in accordance with the velocity of the turbine. It may be noted that the slider 94 will normally remain in the position shown upon a conductive bar 89 at the right-hand end of resistance 9|, but will swingto the left upon the velocity of the turbine exceeding a predetermined value. The bar 89 is provided so that minor accelerations of the turbine will have no effect upon the system.

The network 54 also includes a slidewire resistance 91, the left-hand terminal of which is connected by a conductor 98 to the conductor 93 leading to the intermediate tap 99 on winding 90 and the right-hand terminal of which is connected by a conductor to the right-hand terminal of winding 90. 1 A slider |0| to which the aforesaid conductor 53 is connected cooperates with the resistance 91 to form a follow-up potentiometer |02. The slider |0| is moved along'the resistance 91 by a connection to the gear train 35, and under .control of the motor 34,' the slider movement beingthus concurrent with that of the waste gate 28.

The operation of the electrical control system being set out in detail in the hereinbefore identified co-pending application will be only sunlciently described herein to make clear the need and reason for my present improvements.

The primary windings of all of the transformers 60, 13 and 90 are connected' to the same al ternating current source as the primary 4| of transformer 40. To simplify the drawing, these connections have been omitted. In actual practice, only one transformer needs to be employed, secondary windings 50h, 13b, and 90b being formed as additional windings of transformer 40. In either case, the alternating potentials at the respective terminals of these transformer windings are at all times in phase with each other. The signal potential impressed across the amplifier input terminals 5l and 52 will thus be the algebraio sum of a number of `potentials developed in the three networks 54, 56 and 58.

For convenience in description, the potential conditions existing during a half cycle at which the transformer windings have the polarities indicated by the legends will be considered. For a reference potential the conductor 59 is indicated as grounded, or of zero potential to ground, as shown at |03. Y

In the network 58, then, the slider 64 in the position shown is positive with respect to the center tap of the transformer while the slider 10, being at a mid-point along the resistance 6l, is at a negative potential with respect to the center tap. This network is thus seen to introduce a potential into the series circuit connecting the amplifier input terminals of such polarity as to cause the motor-'34 to rotate and that the slider 10 and conductor 51 are negative with respect to grounded conductor 59.

Turning now to the network 56-` it will be seen that with the snders 11 and as in the position shown, this network introduces into the series circuit a potential equal to the potential of slider 11 with respect to the left terminal of transformer winding 13b. This potential is 'then such that slider 88 and conductor 55 are positive with respect to slider 11.` The potential of conductor 55 with respect to ground depends upon the relative magnitudes of the respectively negative .and positive potentials produced by the networks 58 and 5B. For convenience this potential may be considered to be such that conductor 55 is positive with respect to grounded conductor 59.

Considering finally the network 54, it will be evident that since slider 94 is at the right-hand extremity of the resistance 9|,fthe conductor 93 leading to the tap in the transformer winding 90 is at the same (positive) potential with respect to ground as is the conductor 55, leading to this network. The resistance 91 being connected between this point, or conductor 93, and the now negative terminal of the winding 90, the conductor 53 thus is negative with respect to con# ductor 9,3 by an amount dependent upon the value' 'the effects of networks 56 and 58.

Under such conditions the amplifier input terminal 5| is at the same ground potential as is terminal 52, no signal is then impressed in the amplifier, and the amplifler supplies no current to the motor field winding 36. The waste gate 28 then remains stationary. However,.should any of the sliders be shifted from their positions at which the compound network is balanced a signal potential will develop` across the amplifier' input terminals resulting in thev supply of an operating current to the motor field winding 39 such change the position of the waste gate.

For example, consider the result of a rise in pressure in the engine induction system. The

bellows is then expandedand the slider 11 is moved to the left along the resistance 14, reducing the magnitude of the positive potential introduced bythe network 56 into the series cirx cuit. This positive potential is thus made insufficient to completely cancel or oppose the sum of the negative potentials introduced by the networks 58 and 54 and a signal potential appears at the ampliiler input terminal 5| such that this terminal is negative with respect to terminal 52.

It is assumed that the amplifier and motor are n on the turbine 25, causes the speed thereof to decrease and reduces the compressing effect of the compressor I2. The pressure of the air supplied to the engine i0 and to bellows 80. is now reduced and the slider 11 begins to work hack to the right along resistance 14. The movement of the slider to the left along resistance 01, coincident with the opening movement of the waste gate 20, introduces a balancing positive potential into the series network and this movement will continue until this balancing potential is exactly equalled by the potential introduced by operation of the controller 18 and the series network is again balanced. The motor 34 then stops, leaving the waste gate in the newly selected position.

In similar manner, a decrease in discharge pressure of the supercharger I2 will introduce an opposite potential by action of the controller 18, causing a signal of opposite phase tobe applied to the amplifier which then runs the motor in the opposite direction to close the .waste gate and boost the pressure. Such operation is accompanied by a rebalancing movement of the slider |0| to bring the network to balance again.

The same actions occur upon the movement of either of the manually adjusted sliders 64 and 10, and it will be evident without further description herein that, when properly functioning and energized, the system will permit the selection of any desired discharge pressure for the supercharger under control of c0ntroller,6| and will maintain such pressure by means of controller 18.

The functionlof the controllers 88 and 85 will likewise be apparent, the former serving to introduce a potential into the network such as to open the waste gate 28 when the turbine accelerates at tOo rapid a rate, while the latter causes the same effect if the turbine exceeds a maximum s afe velocity. Such limiting control on the speed and rate of acceleration of the turbo-superoharger unit is effective so long as the electrical circuit is intact and properly energized, and while conditions throughout are Within range of control.

However, the failure of the system for any reason may cause the induction system pressure to rise above a safe maximum and may cause the exhaust back pressure to exceed a permissible value for proper engine operation; or the call of the system for the higher values of induction system pressure may result in the creation of pressures such as to cause damage to the engine'even if only maintained for a short period while the i system accommodates itself to changing conditions.

What is needed, it -will be apparent, is a means responsive to the even momentary rise of the induction system pressure above a selected maximum safe value, or to a condition of overboOst as it is termed, to instantaneously relieve the pressure, independently of the operation of the electrical control system. By use of such means, then, the engine, turbine and supercharger are all positively protected against any such damaging conditions arising.

Still referring to Figure 1 of the drawing, I show in connection with the induction and exhaust system of the engine one practicable means for accomplishing my purpose. The basic units thereofv are a pressure responsive valve |04 and an air motor |05. While the lattermay be a turfbine, bellows or cylinder drive of any suitable kind adjusted to provide a mechanical movement in response to admission of air under pressure, an air turbine is particularly suitable for this purpose.

For purposes of exempliflcation, the valve |04 is shown as comprising an enclosed, box-like casing |06 the interior of which communicates with some point along the route between the discharge side of the compressor |2 and the engine, preferably at a point close to the discharge outlet of the compressor, through a conduitv |01. Thus there is present within said casing |00 ,air under the same pressure substantiallyl as that supplied by the compressor. Within the casing I provide an evacuated bellows |00, one end of which is supported on the casing side wall and the other end of which carries or reciprocates a valve member |09. In response to contraction of the bellows |08 this valve member isvpulled from its seat in a bleed port l I0 in the casing |05, permitting the escape of air from the interior of the casing, and from the conduit I3, into a conduit lll leading to the air motor |05.

Normally, the bellows |00 is expanded to hold the valve |08 to its seat and close the bleed port ||0 to prevent the escape of theI air. For this purpose the bellows |08 may be spring loaded in a well known manner and the force exerted by the spring may be controlled by an adjustment screw ||2 so that the bellows will remain expanded except when the pressure of the surrounding, induction system air is sufllcient' to overcome the spring. Thus it will be seen that the bellows |08 may be adjusted to open the bleed port ||0 instantly when the pressure of the air in the induction system of the engine reaches a selected maximum value so that air can flow under pressure to the air motor |05.

Such admission of the air under pressure to the air motor |05 sets same in operation and as here shown causes movement of a crank ||3 toward the left from the indicated position. The crank ||3 is shown as actuated by a gear box ||4 from the output shaft l I5 of the motor, and the crank is biased by a spring ||6 to normally stand in the position shown. An outlet ||1 is provided in the exhaust stack or conduit 23, as here illustrated ahead of the turbine 2s. and in this outlet is located a relief damper or valve, or second waste gate H8. An arm ||9 is provided for swinging the valve |8 and said arm is connected by a link |20 to the aforesaid crank ||3.

Under normal conditions the valve |04 is closed, the air motor |05 is inoperative and the valve ||0 is closed,.and such conditions maintain as long as the discharge pressure of the compressor |,2 does not exceed a safe value. 'Ihe relief valve ||8 while closed obviously will have no eifect on the operation of the turbine 25, or the control of the waste gate 28 thereover.

Now should the compressor discharge pressure exceed the predetermined maximum safe value, the bellows |08 will be collapsed by the pressure then brought to bear on it, the valve member |08 will open the bleed port ||0 and the air will flow to the air motor |05 setting it in operation to swing the crank H3. The link |20 then swings the arm I9 to open the relief valve |l I0, permitting the exhaust gases to escape lto atmosphere through the outlet ||1. The pressure of the exhaust gases upon the turbine 25 is thus immediately relieved, causing the turbine speed to fall off and the compressor Iz to slowdown and reduce its discharge pressure. As soon as the pressure falls below the safe value again lthe bellows |08 will expand shutting off the flow of air to the motor |05 and the relief valve ||0 will again close. Thus it is evident that I provide simple and fast acting mechanical means for overriding the control system and relieving excess or overboost pressures, and for ensuring that such pressures cannot be developed even if the control system fails entirely.

Referring now to Figure 2 of the drawing, I have shown therein a modified way of accomplishing 9, the end result of the means of Figure 1. In this case, the waste gate 28 in the exhaust stack outlet 21 is shown as operated by an arm |2| which is connected' by a rod |22 to one end of a floating or swinging link |23. The other end of the link |23 is arranged to be oscillated by'a crank |24 on the waste gate motor 34, said crank having a, ringer |25 at its end playing in a slot |25 inthe link for this purpose.

An air motor designated generally at |21 supports and adjusts the link |23 and as herein shown such motor includes a cylinder |28 wherein is arranged a piston |29 having a piston rod |30 projecting from one end of the cylinder and pivotally connected at |3| to the link intermediate its ends. Normally, the piston |29 is urged toward the other end of the cylinder by an expansion coilspring |32 and to this end of the. cylinder is connected a duct |33.

The duct |33 may be connected in any suitable manner to receive air at induction system pressure from the engine when this pressure exceeds the safe value. I have here chosen the duct as communicating with the space between two valve pistons |34 and '|35 arranged in a valve cylinder |35 and connected for reciprocation to a bellows |31 supported by one end in a casing |38. Air from the-induction system is admitted to the casing |38 by a duct |39 and the bellows functions as described in connection with Figure 1. Thus as the pressure rises above the selected maximum, the bellows |31 is contracte-cl, moving the valve pistons |34 and |35 to the right in FigureZ. This action causes piston |34 to seal off an escape port |40 in the wall of the valve cylinder |36, which normally bleeds otr the highl pressure air from the duct |33 and motor cylinder |38, and causes piston |35 to open a port |4| to adinit high pressure air from the casing |38 into the duct |33. When the pressure in the casing |38 falls the expansion of the bellows |31 will return the parts to their normal positions here shown.

In operation, thepiston 29 normally stands in the position illustrated land the air motor thus serves `as a fulcrum mounting for the link |23. Thus opposite swinging movements of the' crank |24, in response to reversal of the waste gate mo tor 34 as previously described, will oppositely swing the link about the pivot connection |3| and oppositely adjust the arm |2| through rod |22 to position the waste gate 28. In the arrangement shown downward movement of the right-hand end of the link |23 opens the waste gate. Now should' 10 in the exhaust outlet 21 is positioned by a crank |42 on the waste gate motor 34, said crank beingh connected by a link |43 to an arm |44 for swing- These are soarranged that it isv possible, by a pull upon the arm |44 such as to extend the strain release spring |45, to swing the waste gate 28 toward open position regardless of action of the motor 34.

An air motor |43 is again provided and in this case comprises a bellows |49 the interior of which is connected bya duct |50 to the valve cylinder |36 of Figure 2 to receive air at induction system pressure therefrom. A spring loaded evacuated compensating bellows |5| is also provided and the two bellows are supported with their free ends at opposite sides of a lever |52 to a lower end of which these ends are pivotally connected by a link |53. The lever |52 is fulcrumed at |54 and at an opposite end has a, finger |55 which plays in a slot |56 in the end of a draw link |51. The opposite ends of the draw link |51 is pivotally connected to the waste gate arm |44.

In operation, as the waste gate 28 approaches its closed position the finger |55'nears the righthand end of the slot |55. Now if the induction system pressure rises above the relief point of the valve of Figure 2, this valve will open and air will ilow from the induction system into the bellows |49. The resulting expansion of the bellows |49 will `swing the lever |52 toward the right at f |51 such as to swing the waste gate 28 toward motors and valves herein shown may be interthe pressure in the inductlonvsystem of the engine rise to a point suiiicient to operate the valve pistons |34 and |35 as has been described, induction system air will ilow into the duct |33 and acting against the piston |29 will urge same downward against the tension of the spring |32 The resulting downward projection of the piston Yrod |30 will then swing or float the. link |23 downward at its right-hand end, the link in such operation pivoting about its connection with the motor crank |24. The waste gate 28 will thus be opened to reduce the turbine speed and relieve the overboost in pressure in the induction system. As soon as this occurs the piston |29 will move back toward starting position to restore the waste gate to normal control by the motor 34. It will be noted that the floating movement of the link, responsive to an overboost condition may override the control of the motor over the waste gate in any position of the latter. I

In Figure 3, I illustrate still -another modiiication olfv my invention, wherein the waste gate 28 Y It is understood that suitable modifications may be made in the structure as disclosed, provided such modications come within the spirit and scope of the appended claims. Having now therefore fully illustrated and described my invention, what I claim to be new and desire to protect by Letters Patent is:

1. Apparatusfor controlling the pressure of the air supplied for combustion in an engine having a turbine driven compressor powered by exhaust gases from the engine, comprising in combination, a valve for varying the pressure differential of the exhaust gases across vthe turbine, control means for positioning said valve in such amanner as to maintain Vthe discharge pressure of the compressor at a selected value within a predetermined range, and means operated by air taken from the compressor when the pressure thereof exceeds a safe maximum value for reducing the pressure diierential of the exhaust gases across the turbine regardless of the position of the said valve.

2. Apparatus for controlling the pressure of the air supplied for combustion in an engine havlng a turbine driven compressor Ipowered by exhaust gases from the engine, comprising in comthegair supplier for combustion in an engine hav.-l ing a turbine driven compressor vpowered by ex.`

haust gases from the engine, comprising in com- 4 bination, a valve for varying the pressure differential of the exhaust gases across the turbine, control means for positioning said valve so that the pressure of the air discharged from said turbine is maintained at a first predetermined value, a second valve operative when opened to reduce the pressure differential of the exhaust gases across the turbine regardless of the position of the iirst mentioned valve, and means operated by air taken from the compressor when the discharge pressure thereof exceeds a second predetermined value higher than said rst predetermined value for opening said second valve.

4. Apparatus for controlling the pressure of the air supplied for combustion in an engine having a compressor for compressing said air, comprising in combination, means for controlling the speed of the compressor. electrical motor means for operating said speed controlling means, an electrical system for operating and controlling said motor means in such a manner as to maintain the air supplied to the engine at a selected pressure within a predetermined range, means connecting the motor means and the speed controlling means and including a floating link swingable about a fulcrum point by operation of said motor means, and means operative by the air delivered by the compressor in response to the pressure of said air rising to a'predetermined value above said range for positioning saidrfulcrum point of the link member in such a direction as to move said speed controlling means to reduce the speed of the compressor.

5. Apparatus for controlling the pressure of the air supplied for combustion in an engine having a` turbine driven compressor powered by exhaust gases from the engine, comprising in combination movable means for controlling the speed of the turbine and compressor, motor means for operating said speed controlling means, an electrical system for operating and controlling said motor means so as to maintain the pressure of the air supplied by said turbine at a iirst predetermined value, means connecting the motor means and the speed controlling means and including a link member having a strain release normally having no effect on the movement of said speed controlling means by said motor means but yieldably restraining movement of said speed controlling the speed o! the compressor, electrically con-.- trolled motor means for operating said speed controlling means, a. current controlling device responsive to a pressure condition of said air,

electrical means including said current controlling device for controlling said motor means to cause the same to control the compressing eilect oi said compressor in such a manner as to maintain said pressure condition at a selected value within a predetermined range, and air operated motor opperatively connected to said speed lcontrolling means and capable of overcoming the effect of said previously'named motor means, and means for supplying a portion oi the air delivered by said compressor to said air operated motor whenever the pressure oi said air exceeds a predetermined value higher than said range.

'1. Apparatus for controlling the pressure of the air supplied for combustion in a combustion chamber of an engine having a turbine driven compressor powered by exhaust gases from the engine, comprising in combination, a valve for varying the pressure diierential of the exhaust gases across the turbine, a motor for positioning said valve, a device responsive to s, pressure condition of said air, means including said controlling device for controlling said motor to `cause the same to position said valve in such a manner aS to maintain the discharge pressure of the compressor at a selected value within a predetermined' range, means including lan air operated device for operating said valve without the aid of said motor in a direction to decrease the pressure differential of said exhaust gases across said turmeans independently of said motor means in a direction such as to reduce the speed of the turbine and compressor, and means for overcoming .said strain release in response to an increase in pressure of the air delivered by the compressor .above a second predetermined value higher than bine, and means for supplying a portion of the air delivered by said compressor to said air operated device whenever the pressure of said air assumes a value which normally indicates that said pressure condition has a value higher than said range.

8. Apparatus for controlling the pressure of the air supplied for combustion in a combustion chamber of an engine having a turbine driven compressorpowered by exhaust gases from the engine, comprising in combination, a. valve for varying the pressure diiIerential of the exhaust gases across the turbine, an electrically controlled motor for positioning said valve, a currentr controlling device responsive to a pressure condition of said air, electrical means including saidcurrent controlling device for controlling said motor to cause the same to position said valve in such a manner as to maintain the discharge-pressure of the compressor at a selected vvalue within a predetermined range, means including an air operated device for operating said valve without the vaid of said motor in a direction to decrease the pressure differential of said exhaust gases across said turbine, and means for supplying a portion of the air deliveredfby said compressor to said air operated `device whenever the pressure of said air assumes a value which normally indicates that said presure condition has a value I higher than said range.

9. Apparatus :tor controlling the pressure o! the air supplied for combustion in a combustion chamber-"of an engine having a compressor ior compressing said air, comprising in combination, means for controlling the speed of the compressor, motor means for operating said-speed controlling means, a. controlling device responsive to a pressure condition oi' said air, means including said controlling device torcontrolling said motor means to cause the same to control the compressing eiIect of said compressor in auch a manner as to maintain said pressure condition at a selected value within a predetermined-range oi absolute pressures, means including an air operated motor and connections between said motor and said speed controlling means for operating said speed controlling means in speed reducing direction if said previously named motor means is not properly operative, and means for supplying a vportion of the air delivered by said compressor to said air operated motor whenever the pressure of said air assumes a value which normally indicates that said pressure condition has a value higher than said range.

10. Apparatus for controlling the pressure oi' the air supplied for combustion in a combustion A chamber of anengine having a compressor for compressing lsaid air, comprising in combination,

pressor, electrically controlled motor means for operating said speed controlling means, a' current controlling device responsive to a pressure condition of said air, electrical means including said current controlling device for controlling said motor means to cause the same to control the compressing eifect of said compressor in such a manner as to maintain said pressure condition at a selected value within a predetermined range oi absolute pressureameans including an air operated motor and connections between said motor and said speed controlling meansforoperating said speed controlling4 means in speed reducing direction if said previously named motor means is not properly operative, and means for. supplying a'portion of the airl delivered by said compressor to said air operated motorwhenever the pressure of said air assumes a value which normally indicates that said pressure condition has a value higher than said range.

11. Apparatus for lcontrolling the pressure of' the airI supplied for `combusion in a combustion chamber of an engine having acompressor for compressing said air, comprising in combination, means for controlling the speed of the compressor, an electrically"` controlled motor means for operating said speed controlling means, a current controlling device responsive to a pressure condition of said air, electrical means including said current controlling device for controlling said motor means to cause the same tofcontrol the compressing effect-of said compressor in such of absolute pressures, means including an air operated device for reducing the speed of said compressor independently of said electrical means `if said previously named motor means is not properly loperative, and means for supplying a portion of the air delivered by said compressor to said air operated motor whenever the pressure of said air assumes a, value which normally indicates means 'for controlling the speed vof the comthat said pressure condition has a value higher than said range.

12. Apparatus for controlling the pressure of the air supplied for combustion in a combustion chamber of an engine having a compressor for compressing said air, comprising in combination. means for controlling the speed of the compressor, an electrical rotary motor for operating said speed controlling means, a current controlling device responsive to a pressure condition of said air, electricalmeans including said current controlling device for controlling the energization of said motor to cause the same to control the compressing eilect of said compressor in such a manner as to maintain said pressure condition at a selected value within a predetermined range Y of absolute pressures, means including an air operated turbine for reducing the speed' of V said compressor if said previously named motor means is not properly operative, and means for` supplying a portion of the air delivered by said com' pressor to said air operated turbine whenever the pressure of said air assumes a value which normally indicates that said presure condition has a value higher than said range.

HUBERT T. SPARROW.

REFERENCES The following references are of record in'the f ille of this patent:

a manner as to maintain said pressure condition 'y at a selected value within a pridetermined range UNITED STATES PATENTS I Great Britain Jan. 3, 1929 

